Multimodal coatings for heat and fire resistance

ABSTRACT

A multimodal coating and method of coating a substrate are disclosed. The coating includes a structural framework: and a medium embedded in the structural framework forming an intumescent coating, the intumescent coating configured to undergo intumescent expansion of an outermost coating of the medium upon heating.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a U.S. National Stage of Application No.PCT/US2019/41099, filed Jul. 10, 2019, which claims priority to U.S.Provisional Application No. 62/696,114, filed Jul. 10, 2018, the entirecontent of both of which is incorporated herein by reference.

STATEMENT OF GOVERNMENT INTEREST

This invention was made with government support from the Air ForceOffice of Scientific Research, contract #FA9550-15-1-0009, and NationalInstitute of Justice, contract #2016-R2-CX-0015. The government hascertain rights in this invention.

TECHNICAL FIELD

The disclosure relates to multimodal coatings for heat and fireresistance.

BACKGROUND

Many materials are subjected to extreme thermal or fire-based stressesalong with mechanical loads, resulting in catastrophic failure withinseconds to minutes, give off noxious gases and lead to death or severedestruction. Current protective coatings or materials are incapable ofprolonged shielding and maintaining structural integrity at temperaturesabove 600° C. and/or are made using environmentally unfriendly methods.For example, materials used in aircraft fuselages are extremely brittleceramic panels and foams, easily degradable carbon composites andaromatic hydrocarbon-based polymers such as polyimides, all of whichprovide minimal protection against fires or thermal stresses and/or canbe costly to synthesize. Damage to these materials is oftencatastrophic, leading to significant loss of time, money and in manycases, life.

In some applications, coatings are applied to surfaces to reduce damagethrough adding an extra layer of protection. These coatings are eitherablative, intumescent, or thick ceramic cements. Ablative coatings arethe current state-of-the-art in aircraft and rocket nozzles; however,they lack the ability to provide prolonged protection in hostileenvironments. Thick ceramic cementitious layers are often bulky, crackeasily when subjected to mechanical stresses, and are prone todistortion and softening due to thermal creep stresses. Intumescentpolymer coatings with clay and ceramic additives, producing insulatingchar by limiting through-thickness thermal transport is currently beinginvestigated. However, the challenges with this technique are poorsurface adherence of the coating, the presence of toxic bio-accumulatorssuch as halogens and bromines that are environmentally unfriendly. Inaddition, the char produced post-fire has poor mechanical resistance toabrasion and humidity, and oftentimes results in ash, presentinglong-term durability issues.

SUMMARY

In view of the above, it would be desirable to developcoatings/materials that are specifically architected to provide thermalprotection by absorbing significant amounts of energy from thefire/heat, while being mechanically operational at hostile temperatures.

In accordance with an exemplary embodiment, a multimodal coating isdisclosed, the coating comprising: a structural framework; and a mediumembedded in the structural framework forming a intumescent coating, theintumescent coating configured to undergo intumescent expansion of anoutermost coating of the medium upon heating.

In accordance with another exemplary embodiment, a method is disclosedof coating a substrate, the method comprising: generating a structuralframework; and embedding a medium in the structural framework forming anintumescent coating, and wherein the intumescent coating is configuredto undergo intumescent expansion of an outermost coating of the mediumupon heating.

In accordance with a further exemplary embodiment, a method is disclosedof coating a substrate, the method comprising: applying an organic witha decomposition temperature tuned between 110° C. to 1000° C. to asubstrate; and adding a waxy layer on an upper surface of the organic,and wherein the organic forms an inner layer, and wherein upon exposureto heat, the inner layer will decompose and outgas, while the waxy layersoften and enables expansion to afford formation of interlayers of poresfilled with gas to reduce thermal conduction.

DRAWINGS

FIG. 1 is a photograph of a Banksia speciosa cone, and its innercross-section revealing the inner structure—the thermally resistantfollicle valve, the seeds encapsulated within the follicle, and the seedseparator membrane flanking the seeds.

FIG. 2 is an image of the Banksia speciosa follicle post-fire, revealingintumescent expansion of the outermost waxy coating, and wherein thetop-right image shows the presence of lignified columns within thecoating, and the bottom images are schematics of the intumescentprocess.

FIG. 3 is a schematic showing the process of a bilayer intumescentcoating producing graphite sheets between organic layers.

FIG. 4 is an imaging showing the optical micrographs and theircorresponding wide-angle scattering images of each layer within thefollicle valve (left image), and the schematic on the right shows asimilarly proposed multi-layered anisotropic composite, and wherein theblack arrow indicates a phonon wave that starts out strongly but as itencounters varying crystal orientations, interfaces, andparticulate/porous architectures, it weakens in intensity and maps out aconvoluted pathway.

FIG. 5 are images showing the mineral coating on the surface of theseed, and wherein the top right image is a top-view of the surface ofthe seed; the bottom-left image is a cross-section showing the locationof the seed coating above an organic substrate containing vital plantorganic; and the bottom-right image is an etched seed mineral plateletshowing the seed crystals in an oriented attachment.

FIG. 6 is an image of a fire in accordance with an exemplary embodiment.

FIG. 7 is an image of a Banksia speciosa cone.

FIG. 8 is an image of an inner cross-section of the Banksia speciosacone revealing the inner structure in accordance with an exemplaryembodiment.

FIG. 9 is a Scanning Electron Microscopy (SEM) image of Species 1 of aBanksia speciosa cone.

FIG. 10 is a Scanning Electron Microscopy (SEM) image of Species 2 of aBanksia speciosa cone.

FIGS. 11A and 11B are a Ca map and SEM image of Species 1.

FIGS. 12A and 12B are a Ca map and SEM image of Species 2.

FIG. 13 is a SEM image of a Non-Pyrophyte species of a Banksia speciosa.

FIGS. 14A and 14B are charts illustrating a map of Ca intensity (a.u.)for Non-Pyrophytic Species, Species 1, and Species 2 in accordance withan exemplary embodiment.

FIG. 15 are X-ray diffraction patterns of a (i) non-pyrophytic, (ii)Pyrophytic Seed—Species 1 and (iii) Pyrophytic Seed Species 2.

FIG. 16 is an optical image of a cross-section of a Pyrophytic Seed,Species 1.

FIG. 17 is an optical image of a cross-section of a Pyrophytic Seed,Species 2.

FIG. 18 is an optical image of a cross-section of a Non-Pyrophytic Seed.

FIG. 19 is an image of Raphide morphology in accordance with anexemplary embodiment.

FIG. 20 is a chart illustrating Calcium Oxalate Monohydrate TGA inaccordance with an exemplary embodiment.

FIG. 21 is an SEM image of a Monoclinic Crystal Morphology in accordancewith an exemplary embodiment.

FIG. 22 is an image showing platelet growth of a Seed Wing (Left),Transition Region (Middle) and Inner Region (Right).

FIGS. 23-25 are image showing platelet growth in accordance with anexemplary embodiment.

FIGS. 26-28 are images showing calcium oxalate.

FIG. 29 is an image showing extra growths on Platelets.

FIG. 30 are images showing an inner structure of the scaffold andplatelets.

FIG. 31 are images inner microcrystalline structure.

FIGS. 32-35 are images of the effect of high temperature annealing andobservation that the organic veneer sheathing the mineral platelets andscaffold begins to degrade, and revealing a highly fibrous substanceunder the calcium oxalate rhomboids.

FIG. 36 is chart illustrating Pyrophytic Seed XRD Temperature comparisonat 400° C., 300° C., 200° C. and RT.

DETAILED DESCRIPTION

The details of one or more embodiments of the presently disclosedsubject matter are set forth in the accompanying description below.Other features, objects, and advantages of the presently disclosedsubject matter will be apparent from the specification, drawings, andclaims.

In accordance with an exemplary embodiment, multiple design componentsare disclosed for coatings or thin panels, that absorb significantamounts of heat and thus, reduce thermal conduction that would otherwiseinduce catastrophic failure to the underlying substrates. Thesesubstrates may include biological materials (skin, hair, DNA, etc.),high performance carbon composites, metals and alloys, and/or timberframes used in construction.

In accordance with an exemplary embodiment, these designs were derivedthrough studies of the woody protective seed pods (follicle valves),seed separator, and seeds of a fire resistant plant (Banksia speciosa),all of which demonstrate incredible resistance to thermal failure uponexposure to fires of temperatures greater than about 600° C. Studieshave yielded a few design criteria that make this translatable to manyapplications, including aerospace, automotive, sports, construction,clothing, etc.

In accordance with an exemplary embodiment, the design aspects include(i) sturdy and durable intumescent coatings composed of thermallymodifiable polymers and mechanical stiffening elements (for example,ceramic, structural biopolymers such as lignin, etc.) that will expandand bubble, and form a protective pocket of gas (air or other) betweenthe thermal source and the underlying substrate, (ii) bilayer coatingscomprised of an additional organic layer (for example, PVA, PAN,biophenols like tannins, etc.), under the intumescent coatings mentionedabove, with potential to graphitize in a reducing environment providedby the intumescent bubbles, (iii) architecting multiple thin layers ofanisotropic insulating and potentially porous materials to disruptcontinuous phonon (thermally induced lattice vibration) transport, (iv)thin coatings composed of metastable material (polymer, ceramic, metal,composite) on the substrate that will absorb heat through endothermicreactions leading to phase transitions, (v) generating sandwichedgraphitic sheets between polymeric/composite/ceramic layers, through theuse of transition metal ions and. nanoparticles, that enable thermalconversion of polymers into ordered graphite, (vi) mechanically andthermally robust ceramic foams filled with reversible phasetransitioning waxes that will aid in energy absorption, and (vii)incorporating environmentally friendly aromatic biopolymers, such aslignin and tannins, into 3D printed designs and electrospun nanofibersthat could be used to generate flexible wearable fabric.

The aforementioned structural designs provide mechanical toughness alongwith thermal shielding to ensure durability and improved damagetolerance at hostile temperatures. These designs are lightweight andflexible for use and include nontoxic chemicals/materials that areproduced under environmentally benign conditions. The utility of thesedesigns can be translated to make structural materials in aerospace orautomotive composites, sports or personal protective gear (for example,armor), construction (building panels that absorb heat), etc.

In accordance with an exemplary embodiment, the coating designs comefrom the investigation of the fire resistant follicle-seed system of theBanksia speciosa, a fire resistant plant species. This system consistsof a woody protective follicle valve encapsulating a protective seedseparator membrane and two seeds.

Through analyses performed at the Kisailus Lab (UCR, Riverside, Calif.),it has been shown that the follicle-seed system is composed oforganic/inorganic components, which, in isolation, are thermally andstructurally degradable at temperatures less than 500° C.; and yet, onaccount of their highly efficient heat retarding surfaces and internaldesigns, survive extended bushfires yielding temperatures of more than600° C.

In accordance with an exemplary embodiment, the following designstrategies were employed by the Banksia speciosa to enable fireresistance:

-   -   (1) A waxy intumescent surface coating in the follicle valves,        which delaminates from the rest of the valve upon heating,        producing localized pores that inhibit flame penetration and        reduce phonon propagation by eliminating conductive pathways.        This coating is strengthened by the presence of lignified        struts;    -   (2) Variations in the orientation of cellulosic-based        crystalline domains that are separated by amorphous matrices        (all within the follicle valve and seed separator structures),        generating complicated and frustrating pathways for heat        transport through phonon scattering and absorption;    -   (3) Structural evolution of the amorphous organic layer (located        beneath the intumescent coating) to dense crystalline carbon,        suggested to be thermally insulating. This carbonization process        is enabled by the inert environments within the intumescent        voids (pores) generated after exposure to fire; and    -   (4) The presence of a thermally absorptive mineral coating on        the surface of the seed, which undergoes endothermic phase        transitions at high temperatures, protect the vital organic        components within the seed.

In accordance with an exemplary embodiment, using the above-mentionedheat resistant designs as inspiration, the following designs aredisclosed, which are thermally resistant:

Durable, Mechanically Robust, Intumescent Coatings

Intumescent composite coatings have the potential to retard heatpropagation from the fire source through to the substrate by expandingand forming insulating pockets of gas. The coatings can containthermoplastic, stiff and hard micro-/nano-structural elements embeddedin a viscoelastic thermally modifiable matrix. The mechanically stiffreinforcements can either be bulk or hollow vertical columnar elementsor inclined struts, composed of either ceramic, metal alloys, graphite,or biophenols. These coatings can also feature hollow/solid cellularfoams or particulate additives strengthening the bubblespost-intumescence, such that they don't break apart into small particleswhen exposed to moisture, gusts of wind, or other loading stresses. Manymaterials (i.e., waxes, hydrogels, and other viscoelastic polymers,featuring either amorphous or semi-crystalline structures), for example,can be used as the intumescent embedding medium. Along with providing anexpanding bubble to thwart phonon transport, these polymer matrices canalso absorb a portion of the thermal energy generated from the source offire to endothermically change its crystallinity/phase, adding yetanother way to dissipate heat. Furthermore, the use of reversibly phasetransitioning waxes adds to the durability of intumescent coatings foruse in environments that may operate at low-to-medium temperatures (fromabout 100° C. to about 300° C.).

However, other coating materials can be realized to achieve higherthermal stability. An example of how to form these coatings is asfollows (FIG. 2):

First, a structural framework was 3D printed composed of either athermoplastic structural biopolymer like lignin, or a hard mineral likealumina. In order to 3D print lignin, dissolve the lignin in a solvent(usually DMSO or ethanol) at 1 wt %.

If needed, binder material like PLA, ABS, or rubber can be used toattain the desired viscosity value, in order to form 3D printed columnsor lattices of desired length and thickness.

After the columnar frames are printed and laid out, the desiredthermally modifiable polymer matrix (for example, waxes that melt atabout 200° C.) or other polymers (for example 88% hydrolyzed PVA thatthermally degrade at about 280° C., solubilized in DI water) was uses asthe embedding medium to form an intumescent coating with structuralelements.

The thickness of this coating using this method can vary from microns tocentimeters, depending on the level of heat it will be exposed to, andthe amount of protection required. Other methods used to deposit thesecoatings, (for example, spin coating, photolithography, etc.) can yieldsignificant thinner coatings (about 1 nm to about 10's of microns).

Depending on the viscoelastic polymer used, a sacrificial layer oforganic can be added between the substrate and the composite coatingbefore adhering it (ideally cellulosic microfibers from cotton plant).This will ensure that upon annealing, the sacrificial layer degrades andoff-gases, producing volatiles (like furfurals in the case of cellulose)in order to allow for expanding bubbles.

In accordance with an exemplary embodiment, if hot molten wax is used,the hot molten wax can easily adhere onto a substrate. This is unlikeother intumescent coatings featuring epoxies that appear to flake offafter hardening.

Multiple other structural reinforcements can be used, including metals,alloys, ceramic, etc. The geometries of these reinforcements can varyfrom being particulate reinforcements can be used, including metals,alloys, ceramic, etc. The geometries of these reinforcements can varyfrom being particulate columnar, hollow/solid, to being foamy withpreexisting interconnected voids.

For example, in accordance with an exemplary embodiment, multiplesubstrates can be used with different surface roughness, curvatures, andgeometries

In accordance with another exemplary embodiment, an alternative andsimplified method is disclosed:

-   -   (1) An organic (for example, oligomer, polymer) with a        decomposition temperature tuned between about 110° C. to about        1000° C., and more particularly about 110° C. to about 600° C.        can be applied to a substrate using either spin coating or dip        coating or spray coating. The thickness of this coating will be        dictated by the viscosity of the organic component but should be        between about 1 nm and about 1 cm.    -   (2) On top of layer 1, a waxy layer can be added using dip        coating, drop casting, melt spinning, spin coating, spray        coating, etc. This wax should have a modifiable viscosity over        temperature ranges of use (for example, from about 200° C. to        about 1600° C.) that can be tuned to expand as needed to        accommodate outgassing.    -   (3) Upon exposure to heat, the inner layer will decompose and        outgas, while the over-layer of wax will soften and enable        expansion to afford formation of interlayers of pores filled        with gas to reduce thermal conduction. The yield of outgassed        material (volume of gas) will determine, in part, the thickness        of the pores formed.        Intumescent Bilayer Coatings with an Underlying Sheet of        Graphite

Additional thermal shielding can be achieved by adding an insulatinggraphitic veneer under the intumescent composite coating discussedabove. Here, a layer is placed of an organic, such as Polyacrylonitrile(PAN), polyvinyl alcohol (PVA), biopolymers such as plant-basedtannin-polysaccharides, etc. of desirable thickness (for example, fromabout 1 nm to about 10 cm) with a proven ability to graphitize in aninert/reducing atmosphere. Upon exposure to heat/fire, intumescence willoccur leaving behind gas pockets. These pockets can contain differentgases (air, carbon monoxide, etc.), on account of the annealing of theunderlying organic layer in a limited supply of oxygen/air. Thisreducing atmosphere in conjunction with the high temperatures from thefire will induce the formation of a graphitic layer from the underlyingorganic, resulting in an intumescent bilayer coating featuring an innerlayer of insulating graphite.

Alternatively, for example, transition metal (for example, Fe, Ni or Co)additives (for example, metal salts, metal ions, metal nanoparticles)can be introduced to the PAN, PVA, tannin-polysaccharide biomass layerto ensure the formation of ordered graphite sheets at relatively lowertemperatures.

In accordance with an exemplary embodiment, one example of how to formthese layers as shown in FIG. 3 can include:

-   -   (1) Dissolve the appropriate polymer (for example, PAN) in a        solvent (dimethyl formamide, DMF) at about 1 wt %.    -   (2) Dip coat (or spray coat) the polymer onto a substrate (for        example, a building panel such as a particle board) to achieve        the desired thickness (for example, about 10 microns). The        concentration of polymer as well as dip coat rate or spray coat        time will dictate thickness.    -   (3) After the first layer is deposited, spray a layer of metal        salts in aqueous solution (for example, Ni Acetate, 10% by wt.        in water) onto the first layer of polymer. A layer of less than        a micron is sufficient but can range from about 1 nm to about 10        microns or more). Additionally, metal nanoparticles can be used        in lieu of metal salts or ions. Metals are typically, but not        limited to, transition metals such as Fe, Ni, Co, etc.    -   (4) Add a second layer of polymer on top of the metal ions or        nanoparticles. Similar to step 2, Dip coat (or spray coat) the        polymer onto the metal ion layer to achieve the desired        thickness (for example, about 10 microns).    -   (5) Multiple layers can be made and do not have to be limited to        polymer-metal ion—polymer architectures, but can include        multiple variations of design and layer thickness.    -   (6) Multiple substrates can be used of different geometries (not        just flat panels but curved structures, fabrics, etc.)

Anisotropic Laminates Featuring Convoluted Thermal TransportationPathways

In crystalline/semi-crystalline heterogenous materials, thermalconduction takes place through phonon transport, i.e. vibrations along acrystalline lattice. When a phonon approaches an amorphous region,thermal attenuation occurs, disrupting, retarding or stopping itstransport. The non-mineralized B. speciosa follicle valve (naturalsystem) uses this strategy of combining highly oriented semi-crystallinepolysaccharide and amorphous phenols to generate convoluted pathways forheat dissipation, thus, achieving remarkable fire resistance.

Flame retardation, especially under prolonged heating conditions, can beachieved by designing architected systems (for example, laminated,cellular, helicoidal, etc.) featuring regions (for example, plies inlamellar or helicoidal structures) with anisotropic (aspectratio—diameter:length—can range from about 10⁶:1 to about 1:10⁶)polymeric/ceramic/metallic structures (from nanoscale to millimeterscale) that are oriented such that they present obstructing directions(for example, 0°-90°; however multiple geometries in 2 dimensions and 3dimensions can be realized) for phonon transport, generating acomplicated heat transport conduit. Geometries can be arranged such thatthe crystalline/fiber orientation is in-plane (for example, usinganisotropic sheets, see FIG. 4), causing the lateral spread of thermaldamage versus through-thickness. However, multiple arrangements can beused depending on how heat needs to be dissipated. The idea is that theorientations of domains can be used to direct phonon transport. Thesedomains can be combined with surrounding matrices (for example,amorphous regions, particle additives, pores containing gases and/orwater) that will further frustrate phonon transport and will lead toenhanced thermal protection.

In accordance with an exemplary embodiment, one example of how to formthese anisotropic layers is as follows:

-   -   (1) Make a suspension of highly anisotropic ceramic or glass        (for example, SiO₂ fibers) nanowires in an aqueous polymer        matrix. (PVA) at about 10 wt % (can range from about 1 wt % to        about 90 wt % or up to maximum viscosity).    -   (2) Print layers using a 3D printer. The rate of deposition will        depend on the viscosity and desired thickness. Alternatives here        include using Langmuir-Blodgett coating, spin coating, dip        coating, melt spinning, electrospinning, centrifugal jet        spinning, spray coating, etc.    -   (3) Subsequent layers can be added, with rotation of the printer        or underlying substrate to achieve the desired orientation. 3D        printers can be used to enable 3 dimensional orientations.    -   (4) Many anisotropic materials can be used: polymers, biological        polymers, ceramics, glasses, metals, composites, etc.    -   (5) Aspect ratios can range from about 10⁶:1 to about 1:10⁶    -   (6) Matrices can be water, polymers, ceramic or metallic        precursors (yielding multiple types of matrix materials and even        interphase reacted materials between the fiber and matrix to        avoid delamination).

Energy Absorptive Phase Transitioning Coatings

As mentioned before, the seeds of the B. speciosa plant feature a thinsurface layer of mineral that, when exposed to high heat,endothermically phase transitions to metastable and stable forms,resulting in energy absorption. This phase change process absorbs asignificant portion of the heat energy generated by the fire source,thus, ensuring that the underlying organic (seed DNA, protein, etc.) isundamaged. Inspired from this design, a coating featuring metastablematerials such as non-flammable hydrous salts, organic polymers,metastable ceramic or metallic materials, with a high thermal tolerancecan be placed at critical regions of structures (i.e., directly incontact with the thermal source or buried within the structure). Toimprove mechanical toughness of these coatings, one can fabricateorganic-inorganic composite phase transitioning coatings to absorbadditional energy. These coatings, through endothermic phasetransitions, will lead to further flame resistance and thermalinsulation. The presence of waxes and lipids will enable reversiblephase transformation.

These coatings can be prepared using a number of techniques. Forexample, it has been shown that the spin coating of inorganic precursorsand anneal to temperatures that yield metastable phases can be used.Alternatively, 3D printing can be used to make pre-architected designsor electrospinning to make lignin-lipid membranes, and/or ceramic-lipidcoatings. Furthermore, one can also use functionalized self-assembledmonolayers (SAMs) of organic molecules to grow oriented crystals ofsilicon carbide, boron nitride, calcium oxalate, attached at a certaincrystalline facet, on required substrates. Using computer-basedsimulations, one can discern which crystalline facet is most thermallyresistant (or hard and abrasion resistant, depending on the application)and ensure that facet is exposed to heat and mechanical loads.

Existing heat shields lack durability, mechanical sturdiness, andstructural stability when exposed to prolonged heat/fire. Novel fireresistant coating designs are disclosed, which are inspired by the B.speciosa plant, which are capable of improving damage tolerance, bothdue to thermal and mechanical stresses.

A major drawback with existing coatings (intumescent or otherwise) isthat they employ no architectural elements to dissipate heat energy. Inaccordance with an exemplary embodiment, coatings are disclosed, whichare carefully architectured coatings employing frustrated phononpathways that will decrease the rate of heat propagation and thus, theprobability of catastrophic failure under thermal stresses is relativelylow. Furthermore, by incorporating both inorganic and organiccomponents, coatings can be created that retard both thermal transportand crack propagation, producing structures that are stable under creeploads. In accordance with an exemplary embodiment, for example, thesematerials can then be used to fabricate jet engine blades, whichcurrently are made of single crystal super alloys, which prove to beboth expensive to manufacture and extremely susceptible to uninhibitedcrack growth.

Overall, the coatings will make protective structures and devices saferby inhibiting flame penetration to the substrate underneath. Using thedesigns to create lightweight insulated wearable fabric will reduce theheat felt by the wearer, and make firefighter uniforms, as well asarmor, comfortable and ergonomic. Another benefit is that this inventionrelates to structural designs, and thus, numerous materials can beemployed as needed, based on the application and operating temperatures.

In accordance with an exemplary, mechanisms of phonon inhibition in thebiological system have been confirmed and the specific advantages ofeach of the regions mentioned are identified in this disclosure. Inaddition, the thermal conductivity of this organism has been measuredversus other plant structures and demonstrated its enhanced thermalresistance. In accordance with an exemplary embodiment, the ability tomake inorganic coatings of metastable ceramic materials (for example,anatase phase TiO2, which transforms to rutile), but are continuing topursue lower temperature materials that require large endothermicreactions to transform has been demonstrated. In addition, the abilityto transform amorphous polymer to graphitic structures but are nowattempting to place these graphitic structures in a lamellar basedstructure has been demonstrated. Furthermore, models have been used todemonstrate the benefit of placing anisotropic materials, orthogonallyto one another, on reduced thermal transport.

In accordance with an exemplary embodiment, optimization parameters suchas material selection, thickness of coating, volume/weight fractions ofmaterial components, etc., were obtained, for example, by utilizing spincoating, 3D printing and electrospinning to create unidirectionalcomposite coatings. These coatings will be applied to construction wood,metals, fabric, etc. and tested with a Bunsen burner for time intervalsranging from a few seconds to about 2 hours to about 5 hours to gaugeperformance under fire/heat, short burns and creep caused by prolongedexposure. In addition, renewable/reusable material-based structures canbe used; for example, lignin “waste” produced during biofuel generationto make heat resistant coatings can be used.

As set forth above, fire related catastrophes devastate the lives andproperties of millions of people each year, necessitating thedevelopment of lightweight fire-resistant protective materials. Inaccordance with an exemplary embodiment, the inspiration for suchmaterials can be found in pyrophytic plants, which have evolvedprotective architectures to shield their seeds and vasculature fromthermal damage as shown in FIGS. 7-36. As set forth, one such structureis a unique phase-transforming biomineralized coating on the surface ofpyrophytic seeds that potentially exhibit an energy absorbing utilityduring a forest fire (FIG. 6).

In accordance with an exemplary embodiment, Scanning Electron Microscopy(SEM) identified the presence of tetragonal platelets on the surface oftwo pyrophytic seeds. Electron Dispersive X-ray Spectroscopy (EDS)mapping revealed that the platelets were calcium-rich. Powdered X-raydiffraction (XRD) identified the platelets to be calcium oxalatebiominerals (phase: monohydrate). In both pyrophytic species, theplatelets are templated across the seed surface by an organic scaffold.Calcium oxalate monohydrate is also identifiable in a non-pyrophyticspecies using XRD.

In accordance with an exemplary embodiment, there was no indication ofcalcium oxalate on the surface of non-pyrophytic species by SEM and EDS.Optical imaging of a cross-section reveals a biomineralized coatingunder an epithelial organic layer. This difference in placement suggeststhat the calcium oxalate has a different utility in pyrophytic andnon-pyrophytic seeds.

Calcium oxalate is thermodynamically metastable and undergoes phasechanges under approximately (˜) 200° C.; the same temperature that mostplant organics begin to degrade. Calcium oxalate is formed in mosthigher plant species either in the monohydrate or dihydrate phase,depending on plant genetics. In plants, the mineral is mainly used as ameans of calcium ion detoxification, although it may also be used as adefense against herbivorous or granivorous predators, or, in pyrophyticseeds, a defense against forest-fires.

In accordance with an exemplary embodiment, the crystals appear to growin size, going from the seed wing region to the inner region featuringthe inner organic components of the seed. The crystals on the innerregion are more reinforced by a fibrous substrate, as well as feature anorganic veneer

Calcium oxalate is formed in plants when a mixture of calcium ions andoxalic acid are pumped into specialized cells called idioblasts. Forexternally formed platelets, for example, the mixture is pumped to theseed surface into a thin organic sheath, which could lead to theformation of excess growths on a platelet's surface, possibly due to themixture pushing out of deformations in the organic sheath.

Organic sheaths are primarily found covering the platelets in themid-seed surface. Concurrently, the platelets formed in the transitionand wing regions are significantly underdeveloped in comparison, whichsuggests that the organic sheaths play a role in the growth of theplatelets possibly by presenting a larger area for nucleation

The platelets in the inner region are fixed to the seed surface byorganic scaffolds. Bleaching the seed sodium hypochlorite revealed thatthe underlying organics holding the platelets are fibrous. Dislocationof the platelets revealed that the scaffolds follow a pattern across theseed surface. The scaffold itself was found to be approximately (˜) 30μm deep and holds onto the bottom half of the platelets.

Demineralization of the platelets with EDTA 8.5 pH buffer revealed theinner microcrystalline structure. This showed a structured growth of thecalcium oxalate on a possible template in which the calcium oxalateforms along rows and columns growing across the short face of theplatelet. Such appearance suggests that the platelets undergo anoriented attachment; which will be further investigated using TEM

Upon annealing the seeds in a muffle furnace to 400° C., it was observedthat the organic veneer sheathing the mineral platelets and scaffoldbegins to thermally degrade, revealing a highly fibrous substrate underthe calcium oxalate rhomboids, possibly functioning as mineral transportchannels

In pyrophytic plants, calcium oxalate is secreted in the monohydratephase. Upon annealing to approximately (˜) 400° C., calcium oxalatemonohydrate is known to endothermically phase transform to calciumcarbonate, as is confirmed in the powder-XRD spectra on the right, andto calcium oxide at approximately (˜) 800° C. This energy absorptivephase transition preserves the vital inner organic components (forexample DNA, proteins, etc.) when exposed to forest fires.

Unless otherwise indicated, all numbers expressing quantities ofingredients, properties such as molecular weight, reaction conditions,and so forth used in the specification and claims are to be understoodas being modified in all instances by the term “about.” As used herein,the term “about” means that the item, parameter or term so qualifiedencompasses a range of plus or minus ten percent above and below thevalue of the stated item, parameter or term. Accordingly, unlessindicated to the contrary, the numerical parameters set forth in thespecification and attached claims are approximations that may varydepending upon the desired properties sought to be obtained by thepresent invention. At the very least, and not as an attempt to limit theapplication of the doctrine of equivalents to the scope of the claims,each numerical parameter should at least be construed considering thenumber of reported significant digits and by applying ordinary roundingtechniques. Notwithstanding that the numerical ranges and parameterssetting forth the broad scope of the invention are approximations, thenumerical values set forth in the specific examples are reported asprecisely as possible. Any numerical value, however, inherently containscertain errors necessarily resulting from the standard deviation foundin their respective testing measurements.

The terms “a,” “an,” “the” and similar referents used in the context ofdescribing the invention (especially in the context of the followingclaims) are to be construed to cover both the singular and the plural,unless otherwise indicated herein or clearly contradicted by context.Recitation of ranges of values herein is merely intended to serve as ashorthand method of referring individually to each separate valuefalling within the range. Unless otherwise indicated herein, eachindividual value is incorporated into the specification as if it wereindividually recited herein. All methods described herein can beperformed in any suitable order unless otherwise indicated herein orotherwise clearly contradicted by context. The use of any and allexamples, or exemplary language (for example, “such as”) provided hereinis intended merely to better illuminate the invention and does not posea limitation on the scope of the invention otherwise claimed. Nolanguage in the specification should be construed as indicating anynon-claimed element essential to the practice ant of the embodimentsdisclosed in the present disclosure.

Groupings of alternative elements or embodiments of the inventiondisclosed herein are not to be construed as limitations. Each groupmember may be referred to and claimed individually or in any combinationwith other members of the group or other elements found herein. It isanticipated that one or more members of a group may be included in, ordeleted from, a group for reasons of convenience and/or patentability.When any such inclusion or deletion occurs, the specification is deemedto contain the group as modified thus fulfilling the written descriptionof all Markush groups used in the appended claims.

Specific embodiments disclosed herein may be further limited in theclaims using consisting of or consisting essentially of language. Whenused in the claims, whether as filed or added per amendment, thetransition term “consisting of” excludes any element, step, oringredient not specified in the claims. The transition term “consistingessentially of” limits the scope of a claim to the specified materialsor steps and those that do not materially affect the basic and novelcharacteristic(s). Embodiments of the invention so claimed areinherently or expressly described and enabled herein.

Certain embodiments of this invention are described herein, includingthe best mode known to the inventors for carrying out the invention. Ofcourse, variations on these described embodiments will become apparentto those of ordinary skill in the art upon reading the foregoingdescription. The inventor expects skilled artisans to employ suchvariations as appropriate, and the inventors intend for the invention tobe practiced otherwise than specifically described herein. Accordingly,this invention includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw. Moreover, any combination of the above-described elements in allpossible variations thereof is encompassed by the invention unlessotherwise indicated herein or otherwise clearly contradicted by context.

It is to be understood that the embodiments of the invention disclosedherein are illustrative of the principles of the present invention. Itshould be understood that the disclosed subject matter is in no waylimited to a particular methodology, protocol, and/or reagent, etc., asdescribed herein. Various modifications or changes to or alternativeconfigurations of the disclosed subject matter can be made in accordancewith the teachings herein without departing from the spirit of thepresent specification. Accordingly, the present invention is not limitedto that precisely as shown and described.

What is claimed is:
 1. A multimodal coating, the coating comprising: astructural framework and a medium embedded in the structural frameworkforming an intumescent coating, the intumescent coating configured toundergo intumescent expansion of an outermost coating of the medium uponheating.
 2. The coating according to claim 1, wherein the structuralframework is a. mechanical stiffening element, the mechanical stiffeningelement being a ceramic and/or a structural biopolymer.
 3. The coatingaccording to claim 2, wherein the biopolymer is lignin.
 4. The coatingaccording to claim 1, wherein the medium is a thermally modifiablepolymer matrix, the polymer matrix being a wax or hydrolyzed polyvinylalcohol (PVA).
 5. The coating according to claim 1, further comprising:a substrate configured to receive the multimodal coating; and an organiclayer under the intumescent layer and on an upper surface of thesubstrate.
 6. The coating according to claim 5, wherein the organiclayer is polyvinyl alcohol (PVA), polyacrylonitrile (PAN), a biopolymer,plant-based tannin-polysaccharides, and/or a biophenol, and wherein theorganic layer is configured to graphitize in a reducing environmentprovided by intumescent bubbles.
 7. The coating according to claim 6,further comprising: a transition metal or an additive in the organiclayer, wherein the transition metal is Fe, Ni, or Co, and the additiveis metal salts, metal ions, or metal nanoparticles.
 8. The coatingaccording to claim 6, comprising: a plurality of alternating layers ofthe organic layer and the intumescent layer.
 9. The coaling according toclaim
 5. further comprising. a plurality of layers of anisotropicinsulating and potentially porous materials configured to disruptcontinuous phonon transport: or a plurality of coatings of a metastablematerial, the metastable material being a polymer, ceramic, metal,and/or composite on the substrate configured to absorb heat throughendothermic reactions leading to phase transitions; transition metalions and nanoparticles sandwiched between polvmeric/composite/ceramiclayers, and wherein the transition metal tons and nanoparticles areconfigured to enable thermal conversion of polymers into orderedgraphite. ceramic foams filled with reversible phase transitioning wavesconfigured to aid in energy absorption, or aromatic biopolymers, such aslignin and tannins, into 3D printed designs and electrospun nanofibersto generate a flexible wearable fabric.
 10. The coating according toclaim 1, wherein the structural framework comprises metals, alloys,and/or ceramics, and the structural framework has a geometry comprisinga particulate, columnar, hollow and solid, and foamy with preexistinginterconnected voids.
 11. The coating according to claim 5, wherein thesubstrate is a plurality of substrates, the plurality of substrateshaving different surface roughness, curvatures, and/or geometries. 12.The coaling according to claim 5, further comprising a metastablematerial being a polymer, ceramic, metal, and/or composite on thesubstrate, where the metastable material absorbs heat throughendothermic reactions as it transitions phases.
 13. The coatingaccording to claim 12, where the metastable material comprises ametastable phase of a metal oxide, a carbide, a nitride, a phosphide, asulfide, and/or an oxalate.
 14. The coating according to claim 13,wherein live metastable material is an anatase phase TiO₂, siliconcarbide, boron nitride, or calcium oxalate.
 15. The coating according toclaim 13, further comprising waxes, where the waxes assist in reversiblephase transitioning of the metastable material.
 16. A method of coatinga substrate, the method comprising: generating a structural framework;and embedding a medium in the structural framework forming anintumescent coating, and wherein the intumescent coating is configuredto undergo intumescent expansion of an outermost coating of the mediumupon heating.
 17. The method according to claim 16, wherein thestructural framework is a mechanical stiffening element, the mechanicalstiffening element being a ceramic and/or a structural biopolymer; andwherein the medium is a thermally modifiable polymer matrix, the polymermatrix being a wax or hydrolyzed polyvinyl alcohol (PVA).
 18. The methodaccording to claim 17, further comprising: depositing the multimodalcoating on the substrate; depositing an organic layer under theintumescent layer and on an upper surface of the substrate, where theorganic layer has the potential to graphitize in a reducing environmentprovided by the intumescent bubbles.
 19. The method according to claim18, wherein the organic layer is polyvinyl alcohol (PVA),Polyacrylonitrile (PAN), a biopolymer, plant-basedtannin-polysaccharides, and/or a biophenol, the method comprising:graphitizing the organic layer in a reducing environment provided byintumescent bubbles.
 20. The method according to claim 19, furthercomprising: adding a transition metal or an additive to the organiclayer, and wherein the transition metal is Fe, Ni, or Co, and theadditive is metal salts, metal ions, or metal nanoparticles.
 21. Themethod according to claim 20, further comprising: adding a plurality oflayers of anisotropic insulating and potentially porous materials,whereby they disrupt continuous phonon transport; adding a metastablematerial, the metastable material being a polymer, ceramic, metal,and/or composite on the substrate, where the metastable material absorbsheal through endothermic reactions as it transitions phases; sandwichingtransition metal ions and nanoparticles betweenpolymeric/composite/ceramic layers, and wherein the transition metalions and nanoparticles are configured to enable thermal conversion ofpolymers into ordered graphite; adding ceramic foams filled withreversible phase transitioning waxes; or generating a flexible wearablefabric by adding aromatic biopolymers, such as lignin and tannins, into3D printed designs and electrospun nanofibers.
 22. The method accordingto claim 21, where step of adding a plurality of layers of anisotropicinsulating and potentially porous materials comprises: suspendinganisotropic ceramic nanowires or glass nanowires in an aqueous polymermatrix; and depositing the ceramic nanowires or the glass nanowires inthe aqueous polymer matrix on substrate by using 3-D printing.Langmuir-Blodgett coaling, spin coating, dip coating, melt spinning,electrospinning. centrifugal jet spinning, or spray coating.
 23. Amethod of coating a substrate, the method comprising: applying anorganic with a decomposition temperature tuned between 110° C. to 1000°C. to a substrate; and adding a waxy layer on an upper surface of theorganic, and wherein the organic forms an inner layer, and wherein uponexposure to heat, the inner layer will decompose and outgas. while thewaxy layer soften and enables expansion to afford formation ofinterlayers of pores filled with gas to reduce thermal conduction. 24.The method according to claim 23, wherein the application of the organicto the substrate is by one or more of the following: spin coaling, dipcoaling, and/or spray coating.
 25. The method according to claim 23,wherein the organic is an oligomer or a polymer.
 26. The methodaccording to claim 23, wherein a thickness of the organic coating isbetween 1 nm and 1 cm.
 27. The method according to claim 23, whereinwaxy layer has a modifiable viscosity over a temperature range of 200°C. to 1600° C., the method comprising: adding the waxy layer by dipcoating, drop casting, melt spinning, spin coating, or spray coating.